The present invention relates to a method for controlling wireless transmission power and a communication channel data rate in a wireless communication system, and particularly preferably applied to a mobile communication system.
In wireless communication systems, there are known techniques for controlling transmission power of a Wireless Communication Station in order to obtain a desired reception quality. For example, U.S. Pat. No. 5,267,262, Qualcomm Inc., “Transmitter Power Control System” discloses a technique in a CDMA mobile communication system as follows. That is, signal received power from each mobile station is measured in a base station. When the measured signal received power is lower than a desired value, an instruction to increase transmission power is transmitted to the mobile station. When the measured signal received power is higher than the desired value, an instruction to reduce the transmission power is transmitted to the mobile station. The mobile station controls the transmission power in accordance with the aforementioned transmission power control instruction. Thus, the received power in the base station is kept substantially constant.
In addition, U.S. Pat. No. 5,559,790, Hitachi Ltd., “Spread Spectrum Communication System and Transmission Power Control Method therefor” discloses a technique as follows. That is, each mobile station measures the reception quality of a pilot signal transmitted with known power by a base station. On the basis of that measuring result, the mobile station transmits a transmission power control signal to the base station for requesting higher transmission power in the case where the reception quality is bad than in the case where the reception quality is good. The base station controls the transmission power of a signal sent to the mobile station, on the basis of the transmission power control signal. Thus, the signal reception quality from the base station is kept substantially constant in the mobile station.
Each of these techniques is aimed at controlling received power or quality on the reception side to be constant. That is, in a transmission power control method using any of the aforementioned background-art techniques, the reception quality is made constant enough to prevent deterioration of reception quality caused by a gain variation in a propagation path or in-system interference caused by unnecessarily excessive transmission power.
However, assume that there is a fading which is a propagation path gain variation having a comparatively short period of time and generated as a mobile station moves. In such a case, when the background-art techniques are used, the transmission power becomes very high when the propagation path gain drops down instantaneously. Thus, average transmission power increases. The increase of the average transmission power increases mutual interference provided for the system as a whole, and results in lowering of communication throughput in the system as a whole. In addition, in a mobile station, the increase of the average transmission power increases power consumption so that the time allowed to talk becomes short.